Range Report Question about grouping...

[z71rat]

I had 1,000 of the Sierra 155gr BTHP bullets to start playing around with to see what kind of accuracy I could get out of my 10PC with them. Here is what I found so far...

I started off at 42.0grs of Varget, and went in .5gr increments to 46.5grs. All of the shots were taken roughly 3 minutes apart after firing several military surplus rounds to heat up the barrel.

The groups started off sub .5MOA at the 42.0grs... WOW!! I was about as tickled as I could be when I saw that!! As the groups continued, the accuracy dropped away significantly between 42.5grs and 43.0grs., and really stunk at 44.0grs. Things got much better at 46.0grs, and started to open back up again afterwards. I stopped at the 46.5grs mark, as that was as far as I had loaded.

All of the groupings were done in 5 shot lots over the course of a few hours. I did it that way to keep the barrel at roughly the same temperature for the duration of testing.

So here is the question: Is the roller coaster effect on the accuracy a common thing?? Or is this out of the ordinary for most barrels??

Thanks for any input or suggestions...

DK

Details:
Savage 10PC .308
factory 18.5" barrel
crowned and threaded with radial brake
virgin primed Federal Estate brass
Varget powder - 42.0 to 46.5 loads
Sierra 155gr BTHP (all weighed out to 155.3grs)
loaded .015 off the lands
unknown velocity at this time
bipod and rear bag support
accuracy from .402 to 1.085

 

[z71rat]

Re: Question about grouping...

The shots that are marked with the "X"'s were the military surplus rounds, and shooting sighters... not for testing purposes.

DK

 

[VKC]

Re: Question about grouping...

Yes, accurate clusters are normal because of barrel harmonics. Find the charge where you get an accurate node, and has the lowest standard deviation of velocity. Look at accuracy ladder testing.

 

[z71rat]

Re: Question about grouping...

Yeah, velocity is something I am gonna have to find out about. I will have to see about gettin a chrony and tryin it out.

Thanks!!

DK

 

[z71rat]

Re: Question about grouping...

I will have to check into some things further, as I am not sure how low of a load I can use and keep it burning consistantly in the case.

For all that matter, I might end up just sticking with the 42.0gr load for a bit!! LOL!! Save some powder, and shoot around 1/2"... not too shabby.

DK

 

[DocB]

Re: Question about grouping...

z,

You may wish to stay with the 45gr. group. Seems to show less vertical than anything else. Horizontal is probably wind or you.

HTH,
DocB

 

[z71rat]

Re: Question about grouping...

All the wind down in the Gulch either hits me in the face, or blows up my pants leg. In this case, the later would be correct.

So the horizontal stringing is preferred over the vertical?? Hmmm, I hadn't thought about that part of it. I always blame anything that doesn't suit me very well as my own fault anyways. I will hopefully get back out there again tomorrow for some more testing. I will let you know how it goes.

With any kind of luck, I will land upon a hotrod round that the 10PC "REALLY" likes, like my old 10FP. I really wish I still had that rifle... but, oh well.

DK

 

[redbullitt]

Re: Question about grouping...

You are looking for the barrel's sweet spot where it is not in its mid whip. You want the velocity that is putting the round out for bore close to the direction change (think peak or bottom of a photo of a sign wave). More vertical ideally means you are putting the bullet out of the bore in a less optimum stage of its vibration.

If you can shoot them cleanly, then definitely go for minimal vertical when looking for a load. Pay attention if you feel like one was your fault and mark it down. No good chasing ghosts lol.

I like the 45 grain group too. I vote check around there in small increments at distance, then play with seating depth.

 

[z71rat]

Re: Question about grouping...

OK, minimum vertical it is. Thanks for the input!!

DK